Hi all posted thread in wrong bit oops.
wondering if anyone can help me i own a 97 P38 4.6 HSE petrol and lpg and its drivig me mad. It has a rebuilt engine with top hats & kent cam I have replaced fuel pump, filters, coils, leads, plugs, all oils then sensers maf, lambas, cam, crank, tp, knock, coolant and finally the idle stepper motor.now this car is driving me mad as it has a bad misfire starting problems and sluggish. Had it plugged in 3 times 1st time no faults.2nd time no faults just a misfire but i noticed the 2 lambas 1 reads 2.5 & 2 reads 4.7.the landy man said check all plugs & leads as autologic cannot detect misfire but did a reset anyway then do a comp test so checked and changed plugs and leads ok still the same. 3rd plug in car ok no electrical faults at all he said its a mechanical fault not electric and running on LPG too much but car takes 5 or 10 min to heat up and change over to LPG. So previous to this i put a lucas cleaner in and he put a cleaner in too. My car wont start 1st time on the turn of the key or it will if you hold it on for about 20 seconds then the revs go to about 1000 then drop to 250rpm or it justs dies.2nd turn off the key starts then up to 2500 rpm.I have noticed the power and trying to chase the misfire. The car has only done 19000 since full rebuild then came power loss, misfire then poor starting/idling can anyone help cheers mike

If it was an oldish car, I would have said choke issue, but not sure about this - does it run ok on gas, once she is started or is it both fuel types?

a valve not opening it will give you a miss fire..

j the range said:

a valve not opening it will give you a miss fire..

Click to expand...

Hydraulic tappet fault??

Thanks all will look into this in more depth runs better on gas than petrol but getting better to start but not great, as just put in valve cleaner in. Just done 140 miles on petrol ooch not cheap as gas

I would say a cam shaft position sensor, will misfire at idle speeds and runs fine at highway speeds....

Hi,
Have you replaced the Throttle Position Censor (a comon problem with the p38) if it is not working properly this will cause all sorts of runing /starting problems.
The cost is around £70.00 (New)and very easy to fit.

Hi Mike
I had problems just like yours on my P38 for a long time and it was driving me mad range rover could not find a falt even after many plugins,so i did a lot of reserch on the net and found that it was the Throttle Position Censor.
This might not sort your problem out but its a good start, the Throttle Position Censor gets cloged up with muck over time and will send the wrong mesage the the ECU,(please look it up on the internet.)

Good luck

Gary